Higher LDL cholesterol levels in the plasma increase cardiovascular risk and reduction in the levels of LDL would decrease CVD risk by a comparable percentage (PNAS, 2009, 106, 9546-9547). Clearance of LDL cholesterol from plasma is through the action of LDL receptors in the liver and LDL receptors are cell surface glycoproteins that bind to apoliporpotein B100 (apoB100) on LDL particles with high affinity and mediate their endocytic uptake (Journal of Biological Chemistry, 2009, 284, 10561-10570). Defect in hepatic cholesterol clearance and elevated levels of plasma LDL cholesterol that result from the mutations cause familial hypercholesterolemia. Such mutations are identified in the human LDL receptor and later in apolipoprotein-B (Nature Structural and Molecular Biology, 2007, 14, 413-419). Recently, mutations within the pro-protein convertase subtilisin/kexin of the subtype 9 (PCSK 9) gene were found to represent a third class of mutations associated with autosomal dominant hypercholesterolemia (ADH). Abifadel et al in 2003 discovered pro-protein convertase subtilisin/kexin of the subtype 9 as the third gene involved in autosomal dominant hypercholesterolaemia (ADH) (Nature Genetics, 2003, 34, 154-156, Trends in Biochemical Sciences, 2008, 33, 426-434). Several mis sense mutations (S127R, D129G, F216L, D374H, D374Y) are associated with hyperdiolesterolemia and premature atherosclerosis (J Lipid Res. 2008, 49, 1333-1343). Loss-of-function mutations (R46L, L253F, A433T) lead to elevated receptor abundance, enhancing clearance of LDL cholesterol from the circulation and reducing cardiovascular risk (Nature Structural and Molecular Biology, 2007, 14, 413-419).
Pro-protein convertase subtilisin/kexin of the subtype 9 belongs to the subtilisin family of serine proteases and its protein structure consists of a pro-domain, catalytic domain, and cysteine/histidine rich C-terminal domain (Structure, 2007, 15, 545-552). Unlike other pro-protein convertases, wherein the pro-domain is further proteolytically processed to activate the serine protease, the pro-domain of secreted subtype remains intact and tightly bound. Within endoplasmic reticulum this enzyme undergoes autocatalytic process which results in release of ˜14 kDa prodomain that remains associated with the catalytic/C-terminal domains, wherein the pro-domain serves as both a folding chaperon and as an inhibitor of enzymatic activity (Journal of Biological Chemistry, 2009, 284, 10561-10570).
It is well documented that epidermal growth factor-like repeat A (EGF-A) of LDLR interacts with this pro-protein subtype mainly with residues 367-381. This EGF-A interaction site is located >20 Å from the catalytic site of this pro-protein subtype. Once EGF-A and this pro-protein subtype interacts they form a complex with the LDLR that enters endosomal pathway and hence LDLR recycling is prevented leading to LDLR degradation. Detailed molecular mechanisms explaining the association of LDLR and this pro-protein subtype and LDLR degradation is not very clear (Drug News Perspectives, 2008, 21, 323-330). Because of inhibition of LDLR recycling, number of LDL receptors on the cell surface are decreased and this increases plasma LDL levels (PNAS, 2009, 106, 9546-9547).
Various approaches for inhibiting this pro-protein subtype are reported, including gene silencing by siRNA or antisense oligonucleotides, mAb disrupting protein-protein interactions or by peptides; all the above-mentioned strategies have shown lowering of LDL cholesterol which may be effective therapy for treating hypercholesterolemia (Biochemical Journal, 2009, 419, 577-584; PNAS, 2008, 105, 11915-11920; Journal of Lipid Research, 2007, 48, 763-767; PNAS, 2009, 106, 9820-9825). However, very little success has been reported in trying to inhibit this pro-protein subtype by using small molecules. Small molecule inhibitors of this pro-protein subtype has its obvious clinical and therapeutic benefit over the other approaches as discussed above for the inhibition of pro-protein convertase subtilisin/kexin of the subtype 9. Small molecule inhibitors of this subtype have been disclosed by us in our application nos. 3556/MUM/2010 & 2292/MUM/2009. We herein disclose novel small molecules which have shown to inhibit the pro-protein convertase subtilisin/kexin of the subtype 9 in in-vitro studies and therefore provides an alternate beneficial approach for treating patients in need of such therapy.